How Do Humans Attempt to Initiate Interaction with a Robot? An Exploratory Study on Multimodal Engagement

In everyday environments, robots must be able to detect when people intend to initiate interaction and to communicate their engagement state in an interpretable manner. Although engagement has been widely studied in human–robot interaction, many existing approaches rely on controlled settings or limited perceptual modalities, leaving open questions about how non-expert users naturally attempt to initiate interaction and how engagement states should be signalled during early interaction. An online pre-study questionnaire with 64 participants was conducted to capture user expectations regarding interaction initiation and engagement feedback. The results indicated a preference for speech- and gaze-based strategies, as well as expectations of clear signals such as robot orientation, verbal acknowledgement, and visual feedback. These insights informed the design of a multimodal engagement system integrating auditory and visual cues and providing incremental feedback to distinguish between attention and confirmed readiness. The system was evaluated in a semi-naturalistic study with 15 participants in a domestic environment. The results show that users were generally able to attract the robot’s attention without prior instruction, while providing minimal information about the robot’s perceptual capabilities led to more consistent interpretation of its engagement responses. The findings provide empirical insight into interaction initiation strategies and highlight the importance of transparent engagement signalling in human–robot interaction.